1. Field of the Invention
The present invention relates generally to a throttle control system for an automotive vehicle by which a throttle valve opening rate is controlled via electrical or pneumatic devices in response to accelerator pedal stroke, and more specifically to a throttle control system provided with fail-safe function.
2. Description of the Prior Art
In an automotive vehicle, when an accelerator pedal is depressed by the driver, a throttle valve disposed in a carburetor is opened to accelerate the vehicle. Conventionally, the relationship between the stroke of the accelerator pedal depressed by the driver and the opening rate of the throttle valve is fixedly predetermined in dependence upon the mechanical structure of the throttle device.
For instance, in the case of a single barrel throttle device, because the throttle valve opening rate is predetermined to be roughly linear in proportion to the accelerator pedal stroke, throttle valve opening rate increases relatively abruptly with increasing accelerator pedal stroke.
These accelerator pedal control characteristics are suitable for accelerating the vehicle quickly, for instance, to avert danger when the vehicle is travelling at a high speed on a highway. However, these are not suitable for repeatedly and finely driving the vehicle a little forward slowly when the vehicle is travelling at a low speed on a busy street. In contrast with this, in the case of a twin barrel throttle device, because the throttle valve opening rate is predetermined to be delayed according to the accelerator pedal stroke, throttle valve opening rate increases relatively gently with increasing accelerator pedal stroke. Therefore, the accelerator pedal control characteristics are suited for repeatedly and finely driving the vehicle a little forward slowly when the vehicle is travelling at a low speed on a busy street. However, these are not suitable for accelerating the vehicle quickly to avert danger when the vehicle is travelling at a high speed on a highway.
That is to say, in the conventional accelerator device, it is impossible to freely obtain appropriate accelerator pedal control characteristics indicative of relationship between throttle valve opening rate and accelerator pedal stroke according to driver's preference or vehicle travelling conditions.
In order to overcome the above-mentioned problems, the same inventer has proposed a novel accelerator pedal control system for an automotive vehicle such that any appropriate accelerator pedal control characteristics representative of relationship between throttle valve opening rate and accelerator pedal stroke can be selected freely by driver's preference according to vehicle travelling conditions, which has already been filed on Dec. 23, 1983 as U.S. Pat. application Ser. No. 564,682 or on Dec. 27, 1983 as EPC patent application No. 83113143.8.
In such a control system as described above, however, since there are arranged a number of electrical or pneumatic devices such as potentiometers, encoders, motors, switches, sensors, etc. between the accelerator pedal and the throttle valve, there exist problems in that the throttle valve is further driven forcibly in spite of the fact that the throttle valve has been fully closed or opened, or the throttle valve is kept open in spite of the fact that the accelerator pedal has fully been released, because these devices operate abnormally due to potentiometer looseness or aging, element failure, etc. When such trouble occurs, some elements of the system may be damaged or the vehicle may be accelerated even after the accelerator pedal has been released.